In recent years, biometric authentication has attracted attention as one of the authentication methods for identifying individuals. A biometric pattern such as a fingerprint has a feature that it does not change even after years of time, and is highly reliable for authentication. Meanwhile, still there is a possibility of unauthorized acts using false biometric patterns such as false fingers, and techniques for preventing such unauthorized acts have also been developed.
For example, the technique disclosed in Patent Document 1 is a technique for determining a false finger with a transparent thin film attached on the surface of a finger. Patent Document 1 discloses a technique of classifying an image region into a plurality of regions including at least a skin region and a background region by using colors of pixels included in a captured image, and using a characteristic of a region that is not classified either as the skin region or as the background region, to thereby determine whether or not a foreign object is present around a finger. According to this technique of Patent Document 1, a foreign object around a finger (a portion having a biological pattern) can be detected.